Cause and causality in daycare research: An investigation of group differences in Swedish child care

One of the most important goals of child care research has been to determine whether or not nonparental care has adverse effects on child development. Answering this question involves making causal attributions about the origins of differences between groups of children who have experienced divergent nonparental care arrangements. Some of the problems researchers face when trying to demonstrate causal relationships are illustrated in this paper using data from the Göteborg Child Care Study, a comprehensive, prospective, longitudinal study comparing the developmental trajectories of children in exclusive home care, family daycare, and center daycare. It is argued that the discovery of significant differences between groups must initiate extensive efforts to validate and interpret the findings. Focusing on the specific characteristics of prospective longitudinal studies, the article shows what measures can be taken to avoid the misinterpretation of group differences that are actually attributable to pre-selection effects or confounding variables. By rigorously identifying such confounds, researchers can accumulate support for hypothesized causal relationships, but they cannot ‘prove’ them because unknown and unmeasured confounding variables may always have important effects.